With reference to FIG. 1, a conventional integrated optical tap monitor 10 in accordance with the present invention includes two waveguides, an input fiber 1 and an output fiber 2, a collimating lens combination 3, a tap filter or tap coating 4, an imaging lenses combination 6, and one photodetecter (PD) package 8, including a PD chip 9.
Light, launched from the input fiber 1, is collimated by the lens combination 3, and directed onto the tap filter or coating 4. A first portion of the collimated beam is reflected by the tap filter or coating 4 to the lens combination 3, which focuses the first portion into the output fiber 2. A second portion of the collimated beam is focused by the imaging lens combination 6 onto the PD chip 9 to monitor the output light power of the input beam.
Unfortunately, any light launched or back reflected from the output fiber 2 will also be focused onto the PD chip 9, providing incorrect measurements of the power of the light portion coming from the input fiber 1.
An attempt at improving the conventional optical tap module is disclosed in U.S. Pat. No. 7,333,693, issued Feb. 19, 2008 to Nagata et al, in which light from the input fiber and light from the output fiber are directed in slightly different directions by an imaging lens. Unfortunately, unwanted reflected light will still enter the packaged photodetector 8, resulting in overly high power readings by the photodetector chip 9 due to multiple reflections off the walls of the photodetector package 8.
An object of the present invention is to overcome the shortcomings of the prior art by providing a lensing arrangement, which separates the light coming from the input fiber and the output fiber, and a mask for preventing any of the light from the output fiber from entering the photodetector package.